Automatic tuning control system



March 1, 1949. E. L. GINZTON ET AL AUTOMATIC TUNING CONTROL SYSTEM 5 Sheets-Sheet 1 Original Filed May 19, 1942 FiGJ OSCILLATOR FILTER PASS SHIFTER PHASE OSCILLATOR March 1, 1949. E. L. GINZTON ET AL 2,462,857

AUTOMATIC TUNING CONTROL SYSTEM Original Filed May 19, 1942 3 Sheets-Sheet 2 FIG.4

TUNED AME BAL. MIXER PHASE INVENTORS: sI-IIFTER EDWARD L. GINZTON WILLIAM W. HANSEN Patented Mar. 1, 1949 AUTOMATIC TUNING CONTROL SYSTEM Edward L. Ginzton, William W. Hansen, and'Russell H. Varian, Garden City, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Original application May 19, 1942, Serial No.

443,604. Divided and this application September 28, 1944, Serial No. 556,194

Claims.

Thisinvention relates, generally, to transmitter and/or receiver circuits wherein means are provided for maintaining oscillators or amplifiers or detectors at an operating frequency determined by a master unit why an incoming signal.

The present applicationis a division of our copending application Serial No. 443,604 for Transmitter and/or receiver circuits, filed May 19, 1942.

In the operation of transmitters and receivers, and especially ultra high frequency transmitters and receivers, it is highly desirable that the transmitters be operated at as nearly fixed frequency as possible and that maximum output be maintained regardless of disturbing influences, such as changes in operating parameters, and that receivers be compelled to follow as closely as possible variations in the frequency of the incoming signal While operating at a maximum output. While the invention is disclosed in connection with ultra high frequency transmitter and receiver circuits it is understood that the same is not limited thereto butcan be applied to other apparatus with equal facility, 1. e., wherever tracking is desired or where maximum ouptut is desired.

One object of the present invention is to provide means for causing the power amplifier of a transmitter to exactly track the oscillator used in conjunction therewith.

Another object of the present invention is to employ a modulation frequency in conjunction Witha power amplifier of a transmitter for causing the transmitter to operate most efficiently for maximum output.

Yet another object is to maintain a tunable device at maximum output by periodically varying its frequency while maintaining its average frequency at a desired value.

A further object is to provide, in conjunction with an oscillator employing cavity resonators, paddle or other movable means for varying the dimensions of said resonators and operated to maintain the oscillator at maximum output.

Yet afurther object of the present invention is to provide a receiver in which amplitude and phase sensitive elements are controlled by means of a modulation frequency imposed either upon the cooperating transmitter or upon the receiver itself to tune the resonant circuits of the receiver to the carrier frequency of the transmitter or to a desired relation with respect thereto.

Other objects and advantages will become apparent fromthe specification, taken in connection with the accompanying drawings wherein the invention is embodied inconcrete. form.

In the drawings,

Fig. 1 is a wiring diagram illustrating a transmitter power amplifier together with means for causing the same to exactly track a master oscillator.

Fig. 2 is an explanatorygraph.

Fig. 3 is a block diagram of receiver means together with means for maintaining the same tunedto the received carrier.

Fig. 4 is a schematic wiring diagram of a practical embodiment of the structure of Fig. 3.

Fig. 5 is a schematic wiring diagram of a modification of the structure shown in Fig. .4.

Fig. 6 illustrates a schematic wiring diagram of a receiver together with means for imposing a modulation frequency thereon for use in maintaining the receiver at the frequency of the received signal.

Fig. 7 is a schematic diagram of a, modification of the structure shown in Fig. 6.

Fig. 8 illustrates schematically the wiring diagram of an oscillator together with paddle means and control means therefor for maintaining a maximized output.

Fig. .9 is an enlarged sectional detail view of a portion of Fig. 8.

Fig. .10 is a sectional view taken along line Ill-4.0 .of Fig. 9.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Fig. 1, the reference numeral I designates an oscillator illustrated as a low power oscillator of the type disclosed inPatent No. 2,242,275, issued May 20, 1941, in the name of R. H. Varian, for Electrical translating system and method, supplied with accelerating voltage from a battery 2. The oscillator I may be used by itself or may be replaced by the upper end of a stabilized frequency multiplication chain such as a crystal controlled chain. Energy is supplied from the catcher resonator I through a concentric line 3 to the buncher resonator 50f a power amplifier 4 of the'type disclosed in the above mentioned patent. Energy from the power amplifier 4 is supplied from catcher resonator 6 thereof through concentric line i and radiated as from a dipole antenna 1' attached thereto.

Intelligence modulation of any desired type may be supplied through leads H and transformer l3 in series with the accelerating voltage battery l4 and connected between the cathode 8 and the buncher resonator .5 of the amplifier 4. If desired, such modulation may be supplied to leads ll, one of which is connected to themodulating grid 9, and the other of which is connected to ground, bearing in mind that the buncher resonator is also connected to ground, as shown. In other words, where the modulation is supplied to leads II, the effective accelerating voltage is varied, whereas if the modulation is supplied the leads I I recurrent variations in the electron stream are obtained through the action of the modulating grid 9.

An oscillator 8, of a frequency higher or lower than the intelligence modulation signal supplied through leads II or II, has its output supplied through a transformer I2 to act between the cathode 8 and buncher resonator 5. Thus, with oscillator 8' operating, the resonant frequency of amplifier 4 is caused to shift at the frequency of the oscillator 8', for example, at the frequency f. A condenser I5 connected across battery I 4 and transformer It enables the output of oscillator 8' to by-pass these elements when the frequency of oscillator 8 is higher than that of the intelligence modulation signal. 7

In the event the intelligence modulation signal is supplied to the leads I I, then in that case the oscillator 8' will not be used but an equivalent oscillator 8" will be used and connected in one of the leads I I' as by use of a switch 9'; a switch 9" is shown for short circuiting the output of transformer I2 in the event that the oscillator 8' is turned off as when oscillator 8 is used. By varying the accelerating voltage or the voltage on the grid 9, as the case may be, at the modulation frequency f, the number of electrons in transit between the grids of the buncher resonator-5 is recurrently varied, which in turn causes the actual resonant frequency of the buncher resonator 5 to vary at the frequency 1. Since the buncher resonator 5 is fed with a constant amplitude carrier frequency wave from oscillator I, there results an amplitude modulation of the energy in buncher resonator 5. A small portion of this energy is fed through a concentric line I6 and is detected by crystal detector I1. The output of detector I! is supplied to a narrow band pass filter I8 which passes only the frequency 1, thus eliminating the second harmonic of the frequency 1 which originates when the buncher resonator 5 is operating at the peak of its resonance curve. This will be apparent from a study of Fig. 2 wherein 1" indicates the resonance curve of the resonator 5 and f designates the wave of frequency f supplied from oscillator 8'.

It will be noted that as the voltage wave of frequency swings to the right of the maximum line m of curve 1' the amplitude of oscillation of resonator 5 and hence the output voltage of detector [1 drops off. Then as the voltage swings to the left back toward the maximum line m, the amplitude of oscillation rises. As the voltage 1 moves toward the left from the line m, the amplitude of oscillation of the resonator 5 again falls off and then as voltage 1 moves toward the right back towards line m, the amplitude of oscillation again rises so that a double frequency Voltage, i. e., a second harmonic voltage of frequency 2 shown in Fig. 2 is produced and this is blocked by the filter I8.

Also, the filter I8 blocks any intelligence modulation so that this filter only supplies the frequency f to the primary IQ of a transformer whose secondary is divided to provide two windings 22 and 22 of a phase discriminator or pushpull circuit having rectifier tubes 24 and 24', the grids of which are connected to the outer terminals ofwindings 22 and 22'. A reference volt- 4 age is supplied directly from oscillator 8' through leads Ill to the grids of tubes 24 and 24 in in phase relation. A phase shifter 2| is shown included in the leads If! to correct any phase displacement caused by transformer I2 and to assure that the reference voltage is in phase coincidence or opposition to the voltages across secondary windings 22 and 22' as will appear.

A bias battery 23 is shown connected in leads I0 between the cathodes of tubes 24 and 24 and their grids. Plate voltage for these tubes is supplied by battery 25 through output resistors 25 and 26'. A direct current amplifier 28 has its input leads 2?, 21' connected across resistors 26, 26' and its output leads 29 have motor windings 3|, 3| of a motor 32 connected in series therein, the rotor of this motor being supplied from a battery 33. The rotor of motor 32 is connected to drive shaft 34 having pinions 36 and 36' thereon engaging the racks of tuning plugs 35 and 35 projecting into resonators 5 and I3. Thus, rotation of motor 32 acts to move plugs 35, 35' through r0- tation of pinions 36, 36, thereby gang tuning these resonators.

In operation, as long as resonator 5 is operating at the peak of its resonance curve corresponding to maximum output from antenna 1' the output of oscillator 8 merely produces the double frequency modulation 2f as shown in Fig. 2 so that no voltage is supplied to transformer primary winding I9. The voltage supplied from oscillator 8' directly through leads II] to tubes 24, 24' produces equal and opposite voltage drops across resistors 26, 26 so that the resultant input to amplifier 28 is zero and the motor 32 remains stationary. However, assume, for example, that the frequency of resonator 5 shifts from its natural frequency down its resonance curve r to the left from its peak to the line marked 1, for example, in

40 Fig. 2. Then the voltage 7 supplied with respect to this line will produce a frequency f in transformer IQ of a predetermined phase as indicated by curve fl in Fig. 2. On the other hand, should the operating frequency of resonator 5 be shifted to the right of its resonance peak of curve r, i. e., to line h, for example, then a voltage of frequency 1 will be produced in the transformer I9 of opposite phase-sense, as indicated by in of Fig. 2. Thus, the device is phase sensitive so that if the operating frequency of resonator 5 should fall below that of its resonance peak :a voltage of frequency f of one phase will be supplied to transformer winding I9 and if it goes above that of its reso-' nance peak a voltage of opposite phase will be supplied to Winding I9. When the operating frequency of resonator 5 falls below its resonant frequency, one secondary winding (for example, winding 22) will produce a voltage of frequency f in phase coincidence with the voltage between leads II). In such case, the output unidirectional voltage of rectifier tube 24 appearing across output resistor 26 will increase. Simultaneously, the voltage across secondary winding 22' will be in phase opposition to that across leads I0, producing decreased unidirectional voltage across output resistor 26 of rectifier tube 25'. The netresult is a unidirectional voltage across leads 21, 21', which is fed to windings 3I, 3I through amplifier 28 in such sense as to retune resonator 5 toward resonance with the input carrier wave.

Conversely, if the input frequency from oscillator I is above the resonant frequency of resonator 5, the phases of the voltages across secondary windings 22, 22 are reversed, producing a unidirectional output voltage between leads 21,

21' "of reversed polarity, and thereby causing motor 32 to rotate'in the opposite direction, again retuning resonator 5 toward resonance with the input wave from oscillator I. Since resonators 5 and 6 are gang-tuned and maintained at the same resonant frequencies, the power amplifier 4 is thus exactly tracked with (kept'in tune with) the oscillator 1, resulting in maximum power output.

'In the receiver structure shown in Fig. 3 an ultra high frequency receiver amplifier H5 is :illustrated having a receiving antenna I I6, this receiver being adapted for use for receiving a modulated carrier which is frequency modulated by a control signal of a frequency outside the intelligence'band. If this receiver is tuned to exact resonance with the received signal no amplitude modulation corresponding to the modulation frequency-f will be produced. However, if the receiver is detuned to one side of the incoming signal there will be amplitude modulation at the frequency f, for when the incoming frequency shifts in one direction the effective mistuning is increased and the amplitude of the receiver amplifier output is decreased, while when the frequency of the incoming signal moves in the opposite direction the mistuning is decreased and the amplitude rises, and hence the output of the receiver amplifier will be amplitude modulated. It will be apparent that-if the receiver is detuned to the opposite side of the incoming signal the same sort of amplitude modulation at frequency will result but will be of reverse phase. The receiver amplifier II5 has its output connected to a frequency detector II1 for detecting the frequency f and theamplitude detector M for detecting amplitude changes at the frequency f. The outputs of the frequencyand amplitude detectors are combined in a phase comparator or mixer II 9, which maybe the same as that shown in Fig. 1 and comprising transformer I9, 22, 22, rectifiertubes 24, 24 and output resistors 26, 26. The output from frequency detector H1 is connected to the leads I0- to serve as a reference voltage, and the reversible-phase output from amplitude detector H8 is connected to primary winding I9. An electromotive force is thereby produced in the output of comparator II9 which is zero when the amplifier II is exactly tuned to the received signal and of one sign when on one side of the peak resonance point and of the opposite sign when on the opposite side of such point. This voltage is used to control the tuning of amplifier H5 in the mannerdisclosedin con- .ection'with Fig. 1 by use of the tuning motor l2! similar to motor 32 of the preceding figure.

A practical example of the structure shown in Fig. 3 is illustrated in Fig. 4 wherein a frequencymodulated signal isreceived, i. e., a signal having a carrier wave which is frequency modulated at the frequency f. This signal is supplied from the receiving antenna to the concentric line I23 and thence into the buncher resonator I24 of a multiresonator-amplifier. Subsequent amplification in resonators I25, I26 is effected and the original frequency modulation results in causing the energy coupledout of resonator I26 by line I21 to be amplitude modulated provided the receiver is mistuned. This amplitude modulation at frequency f is detected by detector I28 and is caused to pass through amplifier I20 which is tuned to the modulation frequency f. The output of amplifier I29 is introducedinto the balanced mixer or phase comparator I30, which may be the same as that in Fig. 1.

The electron beam appearing at the exit opening .of-resonator I2Iiis caused to be split into two equal portions by a wedge plate :I'3I placed at or near cathode potential. The two beams I30 and I30" thus formed are introduced into two resonators I32, I32 respectively, which resonators are tuned by small amounts on either side of the frequency at which the resonators I24, I25, I26 are required to operate. Near the exit openings of the resonators I32, I32 are placed detector grids I33, 133' which are maintained at or near cathode potential. Behind these grids are the collector or detector plates I34, I34 which are connected across series potentiometers I35, I36 whose common junction is at the ground potential. The amount that the resonators I32, I32 are excited (that is, their amplitudes of oscillation) depends upon the exact relation of their resonant frequencies to the frequency'of the Jfield set up in resonators I24, I25 and I26 so that the voltage appearing across potentiometers I35, I36 also depends upon'this relation. This voltage is shown applied to a tuned amplifier I39 tuned to the same frequency as amplifier I29, i. e., to the frequency f, the output of amplifier I39 being likewise applied to the mixer I30. The output of amplifier :I39 acts as a reference voltage similarly to that applied to leads I0 of Fig. 1, so that the unidirectional output of balanced mixer I30 is of one polarity or the other depending upon the proper tuning of the resonators I24, I25, I26 relative to the carrier frequency. The output of mixer I30 is connected to the windings 3| and 3I of the motor 32 which acts to effect tuning through movement of tuning plugs 35, 35 and 35 entering resonators I24, I25, I25. Intermediate frequency amplifier I42 is connected selectively by switch I4I either to leads 24I and thereby to the'detector crystal -I28, to be supplied with the amplified signal appearing thereat, or to leads 242 and thereby to potentiometers I35, I36, to be supplied with the voltage thereacross. These utilization signals after amplification in amplifier I42 and detection by detector I43 and further audio amplification by amplifier I44 are supplied to the utilization device I45.

The system shown in Fig. 5 is similar to that disclosedin Fig. 4 and is also shown applied to a receiver rather than to a transmitter. In Fig. 5 the received frequency-modulated signal is supplied to aresonator I'48 of the receiver tube I46 and is amplifier within resonator I41. A concentric line I52 removes a portion of the energy of resonator I41 and supplies the same to a T-connection I53, part of this energy being detected by a detector I54. The output of detector I54 is supplied to the grids of tubes I59, I59, by way of a common cathode resistor I60. The remaining energy supplied through line I52 is fed through T-connection I 53 to resonators I55, I55 which are resonant to frequencies spaced bya small frequencyinterval on'either side of the desired frequency of operation. The strength of the fields appearing in resonators I55 and I55 is then dependent upon the exact operating point of resonator I'41 with reference to these resonators. The voltages built up across the resonators I55 and I55 are respectively detected by detectors I56 and I56 connected in opposition across the grounded-center-tap resistor I 51. The alternating voltage across each half of this resistor I51 is applied to a respective grid of tubes I59, I59.

.In operation, the frequency-modulated signal applied to input resonator I48 is amplified and appears as a corresponding frequency-modulated fieldin'resonator I41. Aszthis field varies .in frequency, the output from resonator I41, derived by line I52, is amplitude .modulated at the modulation frequency, just as in Fig. 1. This amplitude modulation is of double frequency when resonator I41 is tuned to the carrier frequency of the modulated input signal; but when the resonator I41 is mistuned, the amplitude modulation signal has a component of frequency equal to the input modulation signal at a phase-sense corresponding to the sense of deviation of the resonator frequency from the carrier frequency.

The resonators I55, I55 serve as a frequencymodulation detector, and have an output of the modulation frequency which does not vary in phase and serves as a reference signal.

When resonator I41 is tuned exactly to the carrier frequency, tubes I59 and I59 conduct equally. Accordingly, equal currents flow in the opposedfield windings .231, 23I' of motor 232, and it remains stationary. When a signal of the modulation frequency is detected by detector I54 and applied to resistor 589, it increases the volt- .age on the grid of one of tubes I59, I59 and decreases the voltage on the other grid. This produces an unbalance in the output currents and turns motor 232 in a sense to restore the resonant frequency of resonator I41 to the carrier frequency. When a signal of opposite phase is produced by detector I54, in response to an opposite deviation of carrier frequency relative to the resonant frequency of resonator I41, the sense of unbalance is reversed, and motor 232 turns in the opposite direction, which also restores the frequency of resonator I41 to the carrier frequency. In this way receiver tube I46 is kept at optimum frequency resulting in maximum output, Receiver tube I46 also incorporates an ultra high frequency detector for any signal intelligence modulated upon the incoming carrier, the detected output being derived from lead II and thereby supplied to any suitable utilization device.

In the structure shown in Fig. 6 the receiver tube I BI is maintained at optimum operating frequency, not by means of frequency modulating the transmitter, but by shifting the tuning of the receiver at some convenient frequency. This principle of operation is satisfactory for any fre quency range but is illustrated in Fig. 6 as applied to an ultra high frequency receiver. In this type of electron-beam receiver tube the resonant frequency may be altered by a change in the number of electrons in the electron stream passing through the several resonators. This produces also an amplitude modulation in the main beam. This amplitude modulation can be avoided by injecting an auxiliary electron beam into resonator I62 of tube I6I at right angles to the main beam of the receiver tube and changing the number of electrons in such auxiliary beam synchronously with the changes in the main beam, thereby producing much less amplitude modulation in proportion to the change in resonant frequency obtained. The residual modulation could also be cancelled by inverse modulation of the exciting beam or by such means as disclosed in Patent No. 2,280,824.

The receiver amplifier tube I6I shown in Fig. 6 is illustrated asof the three resonator type having accelerating battery I61, I 61'. The received signal is supplied through line I65 to the buncher resonator I62. having main cathode I66 and auxiliary cathode I12 at right angles thereto. The structure of the amplifier tube I6I is similar to that. which is described in Patent No. 2,439,387

7 a reversing phase-sense.

dated April 13, 1948. An oscillator I10 whose out put control frequency f" is outside of the intelligence frequency band being transmitted supplies, from taps I68, I68 on a potentiometer I69 placed across the oscillator output, a voltage of frequency to the control grids I66 and I13 in front of the two cathodes. There thus appears upon the detector plate I10 of the three resonator amplifier the intelligence signals being transmitted and a control signal of the frequency j, which is preferably chosen to be outside of the band of audio frequency amplifier I16. The signal intelligence frequencies pass on through amplifier I16 to be utilized as in ear phones I11.

The control signal of frequency ,1 passes through tuned amplifier I19 whose output is peaked at the frequency f, and is then applied to a balanced mixer I19. Oscillator I10 also supplies a reference signal passing through phase shifter I88 which reference signal is also supplied to the balanced mixer I19, which may be of the type shown in Fig. 1.

Since the resonant frequency of the resonators I62, I63, I64 is varied periodically at the frequency f, the output of receiver tube I6! will be amplitude modulated at frequency 1 when the central resonant frequency differs from the incoming carrier frequency, and the envelope of this amplitude-modulated Wave will have a predetermined phase-sense when the central resonant frequency is greater than the frequency of the received wave and an opposite phase-sense when the central resonant frequency is less than the received wave frequency. This may be termed When the central frequency is equal to the carrier frequency, an output of frequency 2) is derived. This is the same as in Fig. 1.

The output of the mixer I19 is thus a reversible 4Q polarity, direct current voltage which serves to operate the motor 32 in the proper direction to effect gang-tuning of the resonators I62 to I64, through actuation of the frequency-changing plugs or plungers shown, to maintain the device tuned to the incoming carrier frequency.

In the superheterodyne receiver structure shown in Fig. 7, means is provided for holding the output frequency of a local oscillator I82 of the type disclosed in Fig. 2 of Varian et al. U. S. Patent No. 2,250,511, granted July 29, 1941, at a predetermined frequency difference from the input signal frequency received by the receiver.

' The incoming signal is supplied to a concentric line I83 and is added to the output of the local oscillator I82 in the T junction I84 or any other suitable mixing device. The mixed signals are then detected :by the detector I85. The intermediate frequency output of detector I85 is amplified in intermediate frequency amplifier I86 whereupon its audio component is detected in detector I81. After amplification in an audio amplifier I88, this audio signal is adapted to actuate a utilization device such as ear phones I89.

The accelerating voltage for local oscillator I82 is supplied by a battery I95. An oscillator I93 whose frequency f is above or below the signal intelligence frequency band has its output supplied through transformer I94 for application between the cathode and resonator of oscillator I82.

The system operates to hold the frequency of oscillator I82 so that the intermediate frequency supplied to amplifier I86 is maintained in the middle of the resonance curve of this amplifier. A portion of the output of the detector I81 is supplied to an amplifier I9I tuned to the control frequency f, and from thence to a balanced mixer I92. The tuned amplifier (9| is tuned to pass only the frequency f, thus cutting out any signal intelligence frequency and second harmonics of frequency f. A reference signal of frequency f is supplied directly from oscillator F93 and is passed through the phase shifter I96 to the balanced mixer I92 to serve as a reference voltage. Hence, as in the preceding modifications, the output of the balanced mixer I92 is a reversiblepolarity direct current which is shown used as before for controlling the tuning motor 32 connected to actuate the tuning rod 280. Thus the system operates to keep the beat frequency introduced into amplifier [86 in the middle of the pass band of this amplifier. Inasmuch as the actual phase-reversing signal comes from the intermediate frequency channel the sensitivity of the tuning device depends upon the width of this channel, so that the system is very sensitive to proper tuning and requires very little high frequency amplification.

In the structure shown in Figs. 8 to 10 means is provided for maintaining the two resonators H and 12 of an oscillator 10 at a common frequency. This is accomplished by use of a paddle or vane 86 that extends through an aperture provided in the common wall of resonators H and 12. By varying the position of paddle 86, i. e., projecting the same varying distances within the respective resonators, a differential tuning effect is obtained. This vane is automatically positioned to maintain both resonators at a common frequency through use of concentric lines 16 and 16' coupled to the resonators H and 12, respectively. Voltages proportional to the magnitude of oscillation are thus tapped off and after rectification by detectors 8B and 8B are supplied across potentiometers l1 and H. The taps I8, 18' of these potentiometers are connected to the grids of pushlpull tubes 8|, 8| whose plates are connected to the windings 23l, 23! of the motor 232. By adjusting the taps I8, 18' the desired buncher to catcher voltage ratio may be adjusted at will. Any variations from these ratios will cause energization of the field of motor 232 in the proper direction to effect operation of this motor to cause transverse swinging movement in vane 86 through the driving gearing 83 and 84 and is effective to bring these resonators back to the desired voltage ratios and to a common frequency.

Figs. 9 and 10 show the mechanical details of the structure of the buncher to catcher voltage adjusting vane 86. In Fig. 9, the vane 86 is shown positioned in a slot 9| in the diaphragm 89 separating the resonators H, 12. The vane 86 is supported by a rod 92 pivoted at 85, which pivot is supported by bracket 95, the rod 92 being attached tothe gear sector 84. Since the rod 92 must pass through a slot of the wall 88 of the vacuum tube, the rod is fixedly mounted in end plate 94 which forms the closure of the bellows 93. As shown in Fig. 10 the vane may be of dielectric material instead of metal, if desired.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Whatis claimed is:

1. In a high frequency apparatus, a tube structure having cavity resonators adapted to be excited to oscillation, and means for matching the frequencies of said resonators, said means comprising a paddle member projecting into both of said resonators and a motive means responsive to the amplitude of oscillation of said resonators and adapted to be actuated differentially with respect thereto for controlling the actuation of said paddle member.

2. High frequency apparatus comprising an electron discharge device having a pair of cavity resonators adapted to be excited to oscillation, means for differentially tuning said resonators, and means responsive to deviation of the amplitude of oscillation of said two resonators from a predetermined relation for adjusting said tuning means to restore said resonators to said predetermined relation.

3. An ultra-high-frequency amplifier comprising buncher and catcher resonators, means for passing an electron stream through said resonators, means for supplying a received signal that is frequency-modulated to said buncher resonator for driving the same, and means for keeping said amplifier in tune with said received signal, comprising detector means supplied from one of said resonators, a lower frequency amplifier means coupled to and fed from said detector means for producing a reversible-phase signal depending upon whether the operating frequency of said ultra-high frequency amplifier is above or below that of the received signal, means for splitting said electron beam as the same leaves said resonators, additional resonators tuned to frequencies above and below the optimum operating frequency of said ultra-high-frequency amplifier for receiving said split beam, tuning means for said buncher and catcher resonators, and frequency detector means coupled to and supplied from the output of said additional resonators and receiving said split beam after leaving said additional resonators, and a mixer connected to the outputs of said frequency-detector means and said lowerfrequency amplifier means, said mixer serving to control said tuning means.

4. High frequency electron discharge apparatus comprising means for producing an electron stream, cavity resonator means in the path of said stream and adapted to receive a frequency modulated signal, further means in the path of said stream for dividing said stream into two portions, respective additional cavity resonators in the path of each of said portions and respectively tuned above and below the carrier frequency of said received wave, detector means in the path of each of said stream portions beyond said additional resonators, and means differentially combining the outputs of said detector means whereby said frequency-modulated signal is demodulated.

5. High frequency electron discharge apparatus comprising means for producing a stream of electrons, a cavity resonator in the path of said stream, means along said path for dividing said stream into two portions, and two further cavity resonators, one in the path of each of said portions.

6. High frequency apparatus comprising a cavity resonator, means for exciting said cavity resonator by a wave frequency modulated by a control frequency, frequency discriminator means coupled to said resonator for deriving said control frequency, amplitude detecting means also coupled to said resonator for deriving a reversible-phase alternating wave of said control frequency, phase comparator means energized by said discriminator and said detector, and tuning means controlled by said phase comparator means for controlling tuning of said resonator in a direction corresponding to the phase-sense of said reversible-phase signal, whereby said resonator is maintained in resonance with said frequency modulated wave.

7. A receiver for receiving a radio signal that is frequency modulated, said receiver having a tuned circuit and tuning means for tuning said circuit to the received signal, amplitude and frequency detector means connected to said circuit to be fed therefrom, and a phase comparator connected to both said detector means for comparing the phases of the detected outputs of said detector means and connected to said tuning means for controlling said tuning means in accordance therewith.

8. High frequency wave receiving apparatus comprising a local oscillator for producing a wave of a predetermined frequency, a receiving device for receiving a high frequency wave of frequency different from said predetermined frequency, a mixer coupled to said oscillator and said device for producing an intermediate frequency wave whose frequency equals the difference between the frequencies of said first two waves, means for periodically varying the frequency of said local oscillator wave in response to a control frequency wave, means for detecting said intermediate frequency wave to derive a detected wave of the said control frequency, and means responsive to said detected. Wave and to said control frequency wave for controlling the tuning of said local oscillator, whereby said local oscillator may be maintained at an average frequency having a fixed frequency difference with respect to the frequency of said received wave.

9. The method for maintaining the output Wave of a local oscillator of a superheterodyne receiver at a predetermined difference in frequency from the frequency of an input signal to said receiver comprising the steps of modulating the output wave of the local oscillator with a wave of a frequency that is different from the frequency of the received intelligence signal, mixing the modulated output wave of the local oscillator With the received signal to produce a heterodyne signal, detecting the heterodyne signal to produce a detected signal component of' said different frequency, mixing the different frequency component of said detected signal with a portion of said modulation frequency wave serving as a reference wave, and employing the product of said mixing operation to control the tuning of the local oscillator.

10. In apparatus of the character described, a superheterodyne receiver comprising a local oscillator, means for modulating the output wave of the local oscillator with a wave of a frequency that is different from the intelligence frequency of the received signal, means for combining the received signal with the modulated output wave of the local oscillator to produce a 11. In apparatus for automatically controlling the frequency of a device producing variable frequency energy, the combination comprising means for tuning said device, means for modulating said produced energy at a selected frequency to produce a modulated output wave, means for detecting at least a portion of the moduated output wave of said device, and phase comparator means connected to said modulating means and to said detector means to receive signals from said modulating means and said detector means and connected to said tuning means, for automatically controlling said tuning means.

12. In apparatus for automatically controlling; the operating frequency of a device producing variable frequency wave energy and having means for tuning said device, the combination comprising a source of control frequency wave, means for modulating said wave energy by said control frequency wave, phase shifter means connected to said source for producing a reference signal, means for detecting at least a portion of the modulated energy from said device and obtaining therefrom a demodulated signal of said control frequency, phase comparator means connected to said detecting means and phase shifter means to receive said reference and demodulated signals, and means connecting the output of said phase comparator means to said tuning means.

13. In apparatus for maintaining desired output from a device producing variable frequency wave energy, means for tuning said device, and control means responsive to said output for automatically actuating said tuning means to maintain optimum frequency for maintaining said desired output, said control means comprising means for modulating the energy produced by said device, means deriving and detecting at least a portion of said modulated energy, and means utilizing the output of said last-named means to control said tuning means.

14. In apparatus for maintaining desired output from a device producing variable frequency electric Wave energy, the combination comprising means for tuning said device, an oscillator adapted to be connected to said device to modulate the energy produced by said device, means for detecting said modulated energy, and phasesensitive means connected to said detecting means and said oscillator to be controlled jointly by said modulated energy and the output of said oscillator for controlling said tuning means, to maintain optimum frequency of said device for maintaining said desired power output.

15. In apparatus of the character described, an electron discharge device having a plurality of hollow resonators adapted to have electromagnetic fields therein and means for passing an electron beam through said resonators, means for tuning said resonators to a desired input signal modulated by an intelligence signal, said means comprising motor driven tuning means for tuning said resonators, means for modulating said resonator fields with a wave of a frequency outside of the frequency range of saidintelligence signal band, detecting means for detecting the output of said device, a balanced mixer connected to said detectin means and fed with that component of the detected output derived from said modulation frequency wave, said mixer being connected to said modulating means for receiving energy directly from said modulating means, the

13 output of said mixer being connected to said motive means for controlling said motive means.

16. The method of maintaining a tunable resonant circuit in resonance with a predetermined wave, comprising the steps of applying said wave to said circuit, periodically varying the resonant frequency of said circuit at a control frequency, deriving an amplitude-modulated wave of said control frequency from said circuit, and adjusting the average resonant frequency of said circuit in a direction corresponding to the phase-sense of the envelope of said amplitude-modulated wave.

17. High frequency apparatus comprisin a cavity resonator, means for projecting an electron stream through said resonator, a source of high frequency energy coupled to said resonator, a source of control frequency energy means for controlling said electron stream at said control frequency, detector means coupled to said resonator for producing a wave of said control frequency, phase-comparator means energized by said detector means and by said control frequency source for producing a reversible-polarity output signal corresponding in sense to the sense of deviation of the frequency of said resonator from the frequency of said high frequency energy source, and means for cont1'01ling said resonator frequency by said signal to reduce said deviation.

18. High frequency apparatus comprising a cavity resonator, a source of high frequency wave coupled to said resonator, means for varying the frequency of said resonator periodically at a control frequency, whereby the amplitude of oscillations of said resonator varies periodically with a reversible phase-sense corresponding to the sense of departure of the average resonator frequency from the frequency of said source, means for detecting amplitude variations in the oscillation of said resonator, and control means responsive to said detecting means for adjusting the resonant frequency of said resonator in a sense corresponding to the phase-sense of said amplitude variations, whereby said resonator circuit is maintained tuned with respect to said source.

19. Apparatus for maintaining at maximum output a device adapted to receive a signal, comprising means supplying a modulating potential to said device for modulating said received signal, means for detecting the received signal as modulated by said potential, tuning means for said device, and phase-comparator means for receivin both said detected signal and a reference signal from said modulation-potential supplying means and for controlling said tuning means.

20. The method of maintaining a tunable resonant circuit in resonance with an applied wave, comprising the steps of frequency-modulating said wave by a control frequency wave, applying said frequency-modulated wave to said resonant circuit, deriving a correspondingly amplitudemodulated wave from said resonant circuit having an envelope of a reversible phase-sense corresponding to the sense of departure of the average resonator frequency from the frequency of said applied wave, and tuning said circuit in a direction corresponding to the phase-sense of the envelope of said amplitude-modulatedwave.

21. The method of maintaining a tunable resonant circuit in resonance with a predetermined wave, comprisin the steps of applying said wave to said circuit, periodically varying the relation between the resonant frequency of said circuit ing at said control frequency, and utilizing said output wave to maintain said predetermined wave and said circuit in predetermined relation.

22. In combination, a circuit carrying high frequency oscillations, a low loss resonant element, means for exciting said element with oscillations derived from said circuit, a source of relatively low frequency waves, means for cyclically changing the tuning of said element under control of waves from said source, means for rectifying oscillations derived from said cyclically tuned ele-- ment, means for combining waves derived from the rectified oscillations and waves derived from said low frequency source, and means responsive to the combined waves for changing the relationship between the frequency of operation of said circuit and the average frequency of said resonant element.

23. In combination, a generator of high frequency oscillations, a low loss resonator element,

means for exciting said element with oscillations derived from said generator, a source of relatively low frequency waves, means for cyclically changing the tuning of said element under control of waves from said source, means for rectifying oscillations derived from said cyclically tuned element, a balanced detecting arrangement for combining the rectified oscillations with waves derived from said source of relatively low frequency waves, and means responsive to the output of said balanced detecting arrangement for changing the relationship between the frequency of operation of said generator and the resonant frequency of said resonator element.

24. In combination, a generator of oscillations, a stable circuit tuned to the frequency of oscillations generated by said generator, said stable circuit being coupled to said generator so as to be excited by oscillations generated by said generator, a source of relatively low frequency waves, means responsive to waves from said low frequency source for cyclically varying the tuning of said stable circuit about a desired frequency of operation, a rectifier rectifying Waves derived from said variably tuned stable circuit, a balanced detecting system responsive to and comparing waves derived from said rectifier and from said relatively low frequency source so as to produce a voltage which varies in polarity depending upon departures in frequency of said oscillation generator away from said desired frequency of operation, and instrumentalities responsive to the voltage produced by said balanced detecting sys tem to reduce the relative departure of the frequency of operation of said oscillation generator with respect to the average resonant frequency of said stable circuit.

25. In combination, a generator of high frequency waves of a desired frequency, a stable low loss tank circuit tuned to said desired frequency of operation, a circuit coupling said generator to said tank circuit whereby said tank circuit is excited with waves derived from said generator, a source of low frequency Waves, apparatus operated by said source of low frequency waves for cyclically and continuously changing the tuning of said tank circuit about said desired frequency of operation, a rectifier fed with waves derived from said variably tuned tank circuit, a detecting system supplied with waves derived from said rectifier and said low frequency source, said detecting system operating to combine the waves supplied to it from said rectifier and from said low frequency source to produce a voltage which changes in polarity when the frequency of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,395,987 Round Nov. 1, 1921 1,907,965 Hansell May 9, 1933 2,134,850 Baesecke Nov. 1, 1938 2,251,064

Martin et a1 July 29, 1941 Number 16 Name Date Appleton Jan. 27, 1942 Varian et a1 Sept. 8, 1942 Lindne r .1 Dec. 16, 1941 Ryan May 27, 1941 Terman Aug. 18, 1942 Foster et al Sept. 15, 1942 Dow July 23, 1946 Hansell Jan. 25, 1944 Tawney July 6, 1943 Tunick Dec. 21, 1943 Fremlin May 1, 1945 Litton Dec. 8, 1942 Linder Mar. 23, 1943 Trevor Mar. 2, 1943 Crosby Mar. 21, 1944 Litton Nov. 27,1944

OTHER REFERENCES Ser. No. 363,862, Dolle et al. (A. P. C.) pub. May 

